The invention relates to crosslinkable liquid-crystalline organosiloxanes (LC organosiloxanes) having increased UV resistance, to a process for their preparation, and to their use.
The preparation and use of crosslinkable LC organosiloxanes is known in principle, for example from U.S. Pat. No. 5,211,877 and U.S. Pat. No. 5,362,315. In addition to the mesogens which are the primary factors in determining the properties, these compounds also contain, in adjustable proportions, molecule constituents which firstly contribute to the mesogenic properties of the silicones, but secondly are capable, by means of polymerizable groups, of irreversibly fixing by three-dimensional crosslinking, certain physical and chemical properties which are characteristic of the crosslinked LC silicones thus prepared. Depending on the type and amount of further copolymerizable mesogens and/or chiral compounds and other constituents which participate in crosslinking, it is thus possible to prepare, for example, pigments whose color is based on the cholesteric phase of a copolymerized, optically active mesogen.
Although the LC pigments mentioned in U.S. Pat. No. 5,211,877 and U.S. Pat. No. 5,362,315 satisfy most requirements, they have the disadvantage of being inadequately resistant to UV light.
The object of the invention was therefore to provide crosslinkable building blocks which allow a more favorable construction of molecules suitable for preparation of UV stable LC organosiloxanes.
The invention relates to crosslinkable LC organosiloxanes containing units of the general formula 1
[RbMescSiO(4xe2x88x92bxe2x88x92c)/2]xe2x80x83xe2x80x83(1)
in which
R are C1-C4-alkyl radicals,
Mes is at least one group of the general formula 2 and, if desired, of the general formula 3,
b has the value 0, 1 or 2, and
c has the value 0, 1, 2, 3 or 4,
with the proviso that the sum of the values of b and c is a maximum of 4, where the Mes groups of the general formulae 2 and 3 exhibit the following structure:
xe2x80x94(CH2)pxe2x80x94(O)qxe2x80x94Axe2x80x94[Bxe2x80x94A]rxe2x80x94Exe2x80x94Fxe2x80x94VNxe2x80x83xe2x80x83(2)
xe2x80x94(CH2)mxe2x80x94(O)nxe2x80x94(A)txe2x80x94Qxe2x80x94Xxe2x80x83xe2x80x83(3)
in which
A is a divalent radical from the group consisting of a 1,4-cyclohexylene ring, a 4,4xe2x80x2-bicyclohexylene radical, a 1,4-phenylene ring, a 2,6-naphthylene radical, a 2,7-naphthylene radical, a 2,5-(1,3-dioxanylene) ring and a pyrimidinyl radical,
Q is a radical from the group consisting of xe2x80x94COOxe2x80x94, xe2x80x94OCOxe2x80x94, xe2x80x94Oxe2x80x94, a chemical bond, and xe2x80x94Oxe2x80x94(Cxe2x95x90O)xe2x80x94Oxe2x80x94,
X is a cholesteryl, dihydrocholesteryl, doristeryl, isosorbidyl, isomannidyl or cholic acid radical or an unsubstituted or substituted radical selected from the group consisting of 1,4-phenylene, 4,4xe2x80x2-biphenylyl, 1,4-cyclohexylene, 4,4xe2x80x2-bicyclohexylene, 4,4xe2x80x2-cyclo-hexylenephenylene, 2,5-(1,3-dioxanylene) and pyrimidinyl radicals, where the substituent can be a C1- to C5-alkoxy radical, a C1- to C5-alkyl radical, a cyano radical, a chlorine radical or a nitro radical,
B is a divalent radical from the group consisting of a chemical bond, xe2x80x94Oxe2x80x94CH2xe2x80x94, xe2x80x94CH2xe2x80x94Oxe2x80x94, xe2x80x94CH2xe2x80x94CH2xe2x80x94, xe2x80x94CHxe2x95x90CHxe2x80x94, xe2x80x94COOxe2x80x94 and xe2x80x94OCOxe2x80x94,
E is a divalent radical from the group consisting of a chemical bond, xe2x80x94Oxe2x80x94, xe2x80x94COOxe2x80x94, xe2x80x94OCOxe2x80x94 and xe2x80x94CH2xe2x80x94Oxe2x80x94,
F is a chain of from 0 to 11 CH2 groups, in which individual, non-adjacent CH2 groups may be replaced by oxygen,
VN is a xe2x80x94COOxe2x80x94CHxe2x95x90CH2, xe2x80x94COOxe2x80x94C(CH3)xe2x95x90CH2 or xe2x80x94Oxe2x80x94CHxe2x95x90CH2 group, an oxiranyl group or a xe2x80x94(CH2)uxe2x80x94OCHxe2x95x90CH2 group,
u is an integer from 2 to 8,
m and p are integers from 3 to 7,
n and q are 0 or 1,
t is an integer from 1 to 3, and
r is an integer from 1 to 3,
with the proviso that the combinations of rings A with binding groups B do not constitute phenyl ester derivatives of aliphatic, aromatic or heteroaromatic carboxylic acids.
The invention is based on the discovery that the lack of stability to UV light of the known crosslinkable LC organosiloxanes and crosslinked LC silicones is caused primarily by the use of phenyl carboxylates as mesogen components. Such mesogens are accessible inexpensively and in a technically uncomplicated way by normal esterification reactions. However, on exposure to UV light, phenol esters undergo a rearrangement of these moieties which is known from the literature as the xe2x80x9cFries photorearrangementxe2x80x9d. Even daylight contains sufficient UV light to facilitate this rearrangement.
In this rearrangement, 4-substituted phenyl esters which are used to build up liquid-crystalline phases, or incorporated fragments of these esters in the mesogen, form a mixture of aromatic ketones and other compounds, which are usually relatively strongly colored and in which the substituents originally in the 4-position to the phenol oxygen are moved into other positions which hinder the formation of LC phases. The keto group formed from the carboxyl binding group likewise hinders the formation of LC phases.
The crosslinkable LC organosiloxanes containing units of the general formula 1 avoid mesogen components containing phenyl esters of carboxylic acids. This makes the LC organosiloxanes containing units of the general formula 1 more UV stable. Lateral phenyl substituents, such as, for example, fluorine radicals, in the ortho-positions to 1- and/or 4-substituents do not cause a lack of stability to UV light. The crosslinkable LC organosiloxanes preferably contain from 1 to 70 units of the general formula 1.
In order to achieve particular properties, the compounds according to the invention can be mixed together with isolated further components, for example crosslinking agents, as individual compounds or as mixtures thereof, and/or with further property-modifying, copolymerizable compounds. Examples include chiral compounds which are capable of hydrosilylation for establishing properties such as desired reflection wavelengths. The compounds according to the invention can also be mixed with non-copolymerizable compounds, and crosslinked in their presence.
The additional copolymerizable crosslinking agent components can be known compounds, preferably carrying a terminal and thus hydrosilylation-capable double or triple bond at one end of elongate molecules, and a crosslinkable group, such as the acryloyl radical or the methacryloyl radical, at the other end. These compounds conform, for example, to the general formula 4
CH2xe2x95x90CHxe2x80x94(CH2)pxe2x88x922xe2x80x94(O)qxe2x80x94Axe2x80x94[Bxe2x80x94A]rxe2x80x94Exe2x80x94Fxe2x80x94VNxe2x80x83xe2x80x83(4)
in which A, B, E, F, VN, p, q and r can adopt the meanings given for the general formulae 2 and 3, where, if necessary, proportions of additional crosslinking agent components which may also contain phenol ester groups can also occur here if the UV stability of the system as a whole is not thereby impaired, but other, desirable properties, such as, for example, a low glass transition temperature and/or a higher crosslinking density of crosslinked LC organosiloxanes prepared therewith can be achieved. An example of a compound of this type is 4-methacryloyloxyphenyl-4-allyloxybenzoate, known from WO 94/09086.
In addition, further mesogenic or non-mesogenic compounds containing at least one and optionally a plurality of polymerizable groups can be admixed with the organosiloxanes according to the invention and reacted together therewith to give a three-dimensionally crosslinked, insoluble LC substance, such as a pigment. Examples of such compounds are crosslinking agent components of the general formula 5
CH2xe2x95x90CHxe2x80x94(CH2)pxe2x88x922xe2x80x94(O)qxe2x80x94Axe2x80x94[Bxe2x80x94A]rxe2x80x94Exe2x80x94Fxe2x80x94VNxe2x80x83xe2x80x83(5)
in which A, B, E, F, VN, p, q and r have the meanings given for the general formula 2; bisacrylates or bismethacrylates of mesogenic compounds of the general formula 6
VNxe2x80x94(CH2)rxe2x80x94[Mxe2x80x94A]txe2x80x94Mxe2x80x94(CH2)rxe2x80x94VNxe2x80x83xe2x80x83(6)
in which
M is an oxygen atom, a carboxyl group or an oxycarbonyl group, and
VN, A, r and t can adopt the above meanings. These can be employed alone or as a mixture of various compounds of the general formulae 5 and 6 or as a mixture with non-mesogenic bisacrylates and/or bismethacrylates.
In the general formula 5,
p preferably has a value of from 3 to 6,
a preferably has the value 0, 1 or 2,
A is preferably a 1,4-phenylene radical, and
VN is preferably a methacryloyl radical.
Examples of non-mesogenic compounds which can be used as additional components are bisacrylates and bismethacrylates of straight-chain or branched aliphatic or cycloaliphatic diols or triols or of polyethers; trismethacrylates or bisvinyl ethers of aliphatic diols. These may be used individually or as mixtures of such compounds.
In addition, the LC organosiloxanes according to the invention can also be mixed with substances which contain no polymerizable groups and function as external plasticizers in the substance formed after the polymerization. Examples of compounds of this type are phthalic diesters, sebacic diesters or other compounds usually used for this purpose.
Before crosslinking, the liquid-crystalline organosiloxanes can also be mixed with further property-modifying, copolymerizable compounds, for example further chiral, hydrosilylation-capable or non-hydrosilylation-capable compounds in order to establish targeted properties, such as desired reflection wavelengths. It is likewise possible to admix coloring compounds.
Owing to their desirable properties, in particular increased elasticity of products produced therewith, easier access to the compounds, and greater brightness of the colorants produced therewith, preference is given to compounds of the general formula 1 in which
R is a methyl radical,
m and p are integers from 3 to 5,
X is a cholesteryl radical, a doristeryl radical, an isosorbidyl radical or an unsubstituted or 4-substituted phenyl radical whose substituents are C1- to C3-alkoxy radicals, C1- to C3-alkyl radicals, a cyano radical or a nitro radical, and
B is a chemical bond or an xe2x80x94Oxe2x80x94CH2xe2x80x94, xe2x80x94CH2xe2x80x94Oxe2x80x94or xe2x80x94CH2xe2x80x94CH2xe2x80x94 group.
The UV-stable organosiloxanes according to the invention are preferably open-chain, cyclic or silsequioxanes, more preferably cyclic siloxanes.
The UV-stable, highly crosslinkable, liquid-crystalline organosilicones according to the invention can be prepared by processes known in principle by reacting organosilicon compounds containing units of the general formula 7
xe2x80x83[RbHcSiO(4xe2x88x92bxe2x88x92c)/2]xe2x80x83xe2x80x83(7)
in which R, b and c have the meanings given in the general formula 1, preferably in the presence of at least one metal from the platinum group and/or compounds thereof, with compounds of the general formulae 5 and, if desired, 8
CH2xe2x95x90CHxe2x80x94(CH2)mxe2x88x922xe2x80x94(O)nxe2x80x94(A)txe2x80x94Qxe2x80x94Xxe2x80x83xe2x80x83(8)
in which A, Q, X, m, n and t have the meanings given for the general formula 3.
The novel feature of the compounds of the general formula 5 is that they have at one end of the preferably rod-shaped molecule a terminal double bond which can be hydrosilylated, but at the other end have a polymerizable group which has different reactivity from the olefinic group and which is crosslinkable, but does not hinder the hydrosilylation of the olefinic double bond.
The above reaction is preferably carried out in the presence of least one metal from the platinum group and/or compounds thereof as catalyst. The total number of moles of the compounds of the general formulae 7 and 8 corresponds, depending on the respective reactivity, to 0.75 to 1.25 times the total number of all Sixe2x80x94H bonds in the organosiloxanes of the general formula 7.
The composition of the compounds of the general formulae 7 and 8 is freely selectable, with the proviso that at least one Sixe2x80x94H bond of the silane of the general formula 5 is reacted with a compound of the general formula 8.
Examples of auxiliaries are known inorganic or organic pigments, adhesion promoters, further polymers, emulsifiers, stabilizers and other, usually conventional additives.
Examples of metals from the platinum group and/or compounds thereof, referred to below as the hydrosilylation catalyst, which can effect the process according to the invention are platinum, palladium, rhodium, iridium and compounds thereof, preferably platinum and/or compounds thereof. All catalysts which have also been employed hitherto for the addition of hydrogen atoms bonded directly to silicon atoms onto aliphatically unsaturated compounds can be employed here. Examples of such catalysts are metallic and finely divided platinum, which can also be on supports, such as silicon dioxide, aluminum oxide or activated carbon, compounds or complexes of platinum, such as platinum halides, for example PtCl4, H2PtCl6.6H2O, Na2PtCl4.4H2O, platinum-olefin complexes, platinum-alcohol complexes, platinum-alkoxide complexes, platinum-ether complexes, platinum-aldehyde complexes, platinum-ketone complexes, including products of the reaction of H2PtCl6.6H2O and cyclohexanone, platinum-vinylsiloxane complexes, in particular platinum-divinyltetramethyldisiloxane complexes with or without a content of detectable inorganically bound halogen, bis(gamma-picolinyl)platinum dichloride, trimethylenedipyridinylplatinum dichloride, dicyclopentadienylplatinum dichloride, (dimethyl sulfoxide)ethyleneplatinum(II) dichloride, and products of the reaction of platinum tetrachloride with an olefin and a primary amine, secondary amine, or both primary and secondary amines, such as the product of the reaction of platinum tetrachloride dissolved in 1-octene with sec-butylamine, or ammonium-platinum complexes.
The hydrosilylation catalyst is employed in effective amounts, preferably in amounts of from 0.05 to 0.50 mmol, in each case calculated as elemental platinum and based on the number of moles of the reaction components, i.e., the compound(s) of the general formula 2 or 3 or the siloxane derivatives containing at least one hydrogen atom bonded directly to silicon, which is/are present in a sub-stoichiometric or stoichiometric amount.
The reaction is preferably carried out at temperatures of from 0xc2x0 C. to 150xc2x0 C., preferably at pressures of from 0.05 MPa to 2.0 MPa. If the siloxane of the general formula 7 or the compound(s) of the formulae 5 and/or 8 are very slow to react, the process can also be carried out at elevated temperatures, higher pressures and in the presence of more platinum catalyst.
The reaction is preferably carried out in a solvent, which is preferably aprotic. Solvents or solvent mixtures having a boiling point or boiling range of up to 160xc2x0 C., preferably up to 120xc2x0 C., in each case at 0.1 MPa (abs.), are preferred. Examples of solvents are esters such as methyl acetate, ethyl acetate, n-propyl and isopropyl acetate, n-, sec- and t-butyl acetate, ethyl formate and diethyl carbonate; ethers such as dioxane, tetrahydrofuran, diethyl ether, di-n-propyl ether, diisopropyl ether, di-n-butyl ether, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol dimethyl ether. and anisole; chlorinated hydrocarbons such as dichloromethane, trichloromethane, tetrachloromethane, 1,2-dichloroethane, trichloroethylene, tetrachloroethylene, and chlorobenzene; hydrocarbons such as pentane, n-hexane, hexane isomer mixtures, cyclohexane, heptane, octane, petroleum benzine, petroleum ether, benzene, toluene and xylenes; ketones such as acetone, methyl ethyl ketone and methyl isobutyl ketone; and mixtures of these solvents.
The term solvent does not necessarily mean that all the reaction components must dissolve therein. The reaction can also be carried out in a suspension or emulsion of one or more reactants. The reaction can also be carried out in a solvent mixture having a miscibility gap, where in each case at least one reactant is soluble in each of the mixture phases.
The LC organosiloxanes can be three-dimensionally crosslinked by means of free radicals or by photocrosslinking, if desired as in admixture with additives. The crosslinked LC organosiloxanes can be employed as pigments or for the production of optical elements, such as structured filters, polarizers and retardation plates.
The preparation of the compounds of the general formula 5 is known, for example from U.S. Pat. No. 5,221,759.
In the examples below, unless otherwise stated, all amounts are based on weight; all pressures are 0.10 MPa (abs.); and all temperatures are 20xc2x0 C. The following abbreviations are used: C=crystalline; N=nematic; S=smectic; m.p.=melting point; and BHP=2,6-di-tert-butyl-4-methylphenol.